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When Listeria attack the intestinal microbiota

The intestinal microbiota contributes to our health in many different ways, including the establishment of a first barrier against orally acquired infectious pathogens. In a study published on 2 May 2016 in the Proceedings of the National Academy of Sciences, the team of Javier Pizarro-Cerda at the Joint Research Unit for Bacteria-Cell Interactions headed by Pascale Cossart (INRA, Institut Pasteur, INSERM) demonstrates that epidemic strains of the bacterial food-borne pathogen Listeria monocytogenes secrete a toxin that alters the host intestinal microbiota and promotes infection.

Observation by fluorescence microscopy of a cell infected by Listeria. © Institut Pasteur, Edith Gouin, Matteo Bonazzi
Updated on 06/02/2016
Published on 05/27/2016

Listeria monocytogenes is a Gram-positive bacterium that causes food-borne infections in humans and animals. Upon consumption of contaminated food, L. monocytogenes reaches the intestinal lumen, crosses the intestinal barrier and disseminates within the host. The clinical manifestations of listeriosis vary from mild, self-limiting gastroenteritis to severe intestinal and systemic infections, with a fatality rate estimated at 20-30% of infected individuals. The host gut microbiota plays a critical role in resistance against colonization by invading pathogens within the intestine, but the mechanisms displayed by L. monocytogenes to compete with the host microbiota to survive in the intestine were unknown.

The most severe listeriosis outbreaks are associated with a subset of L. monocytogenes epidemic clones. The team of Javier Pizarro-Cerda identified that the Listeriolysin S, a toxin secreted by this group of epidemic bacteria, contributes to the survival and virulence of L. monocytogenes in a murine oral infection model. The researchers determined that Listeriolysin S is expressed exclusively in the intestine of orally infected animals, and that this toxin displays antibiotic activity against a narrow spectrum of bacteria. In collaboration with the Center of Bioinformatics, Biostatistics and Integrative Biology (C3BI), and with the Center for Innovation & Technological Research (CiTech), the researchers showed that expression of Listeriolysin S correlates with a decrease in microbiota species (Alloprevotella and Allobaculum) which are protective against bacterial intestinal infections.

Since its discovery in 1926, the L. monocytogenes virulence factors have been shown to exert their activity by targeting host cells and tissues or by protecting bacteria from host factors. This study demonstrates for the first time that epidemic L. monocytogenes are able to target the host intestinal microbiota by secreting a novel antibiotic, and highlights potential similarities to other enteric infectious diseases. This work enhances in particular our current understanding of why only a subset of L. monocytogenes strains are associated with epidemic outbreaks.


Juan J. Quereda et al. Bacteriocin from epidemic Listeria strains alters the host intestinal microbiota to favor infection, PNAS, 2 May 2016